(a) Technical Field
The present invention relates to a water trap device for a fuel cell vehicle. More particularly, the present invention relates to a water trap device for a fuel cell vehicle, which can simultaneously discharge residual hydrogen from a fuel cell stack and residual coolant collected in a water trap.
(b) Background Art
In a fuel cell stack for a fuel cell vehicle, a membrane electrode assembly (MEA) is positioned at the most inner portion, the MEA including a solid polymer electrolyte membrane capable of transporting hydrogen protons, and catalyst layers, i.e., an anode and a cathode, formed on both sides of the electrolyte membrane to allow hydrogen and oxygen react with each other.
Moreover, a gas diffusion layer (GDL) is positioned at the outside of the MEA, i.e., on the surface where the cathode and the anode are positioned, and a separator having flow fields for supplying fuel and exhaust water produced by the reaction is positioned at the outside of the GDL.
Accordingly, an oxidation reaction of hydrogen occurs at the anode of a fuel cell to produce hydrogen ions and electrons, and a reduction reaction of oxygen occurs at the cathode receiving the hydrogen ions and electrons from the anode to produce water.
That is, hydrogen is supplied to the anode (also referred to as an oxidation electrode) and oxygen (air) is supplied to the cathode (also referred to as a reduction electrode). The hydrogen supplied to the anode is decomposed into hydrogen ions (protons, H+) and electrons (e−) by a catalyst of the electrode layer provided on both sides of the electrolyte membrane. At this time, only the hydrogen ions (protons, H+) are transmitted to the cathode through the electrolyte membrane which is a cation exchange membrane and, at the same time, the electrons (e−) are transmitted to the anode through the GDL and the separator, which are conductors.
Accordingly, at the cathode, the hydrogen ions supplied through the electrolyte membrane and the electrons transferred through the separator meet the oxygen in the air supplied to the cathode to cause a reaction to produce water.
Here, electrical energy is generated by the flow of the electrons through an external conducting wire due to the transfer of the hydrogen ions, and heat is additionally generated during the reaction.
Meanwhile, when an insulator which transfers the hydrogen ions to the oxygen supplied to the cathode is in a dry state, not in a wet state, the hydrogen ions are hard to transfer. Accordingly, moisture, i.e., deionized water for humidification is additionally required other than the water produced by the oxygen.
To this end, coolant for cooling and humidification flows in the fuel cell stack. Here, it is necessary to maintain the balance of the coolant so as not to cause a water shortage in the gas (hydrogen and oxygen) supplied to the fuel cell stack.
In general, since the water shortage affects the performance of the fuel cell stack and causes deterioration, the amount of water discharged to the outside of the fuel cell stack is designed to remain constant.
Accordingly, the residual coolant is collected in a water trap and, if the amount of the collected coolant exceeds a predetermined level, the coolant is automatically discharged to the outside. Here, if the residual coolant is not discharged smoothly, it affects the humidification balance, thus deteriorating the performance of the fuel cell stack.
Meanwhile, hydrogen supplied from a hydrogen tank is mixed with unreacted hydrogen discharged through an anode outlet line after the reaction in the fuel cell stack, and the mixed hydrogen is supplied to a hydrogen inlet of the fuel cell stack.
However, if the hydrogen discharged from the anode outlet line is continuously recirculated, the hydrogen density may be reduced. Accordingly, the hydrogen may be designed so as not to be recirculated, being discharged through a hydrogen vent valve and a silencer in accordance with a predetermined control logic.
The structure of a conventional water trap device and the operation of discharging residual coolant using the water trap will be described below.
FIG. 2 is a schematic diagram illustrating a conventional water trap device.
An anode outlet line 10 (hydrogen discharge line) mounted in a dispenser of a fuel cell stack 100 is connected to a hydrogen vent valve 40 and a silencer 50 in turn, and a coolant outlet line 30 of the dispenser of the fuel cell stack is connected to a water trap 20.
Moreover, a moisture removal line 60 for discharging moisture droplets contained in hydrogen to the water trap 20 is connected between the top of the water trap 20 and the anode outlet line 10.
First and second level sensors 70a and 70b are mounted on upper and lower portions of the water trap 20 respectively, and a water trap outlet valve 80 is mounted on a lower portion thereof.
Accordingly, when the first level sensor 70a detects a higher coolant level, the water trap outlet valve 80 is opened to discharge water. On the other hand, when the second level sensor 70b detects a lower coolant level, the water trap outlet valve 80 is closed.
The reason why the coolant is left in an amount that can be detected by the second level sensor 70b is to prevent the hydrogen discharged through the anode outlet line 10 from being discharged to the water trap 20 through the moisture removal line 60 for removing coolant moisture contained in the hydrogen in the anode outlet line 10. Accordingly, the hydrogen discharged through the anode outlet line 10 is transferred to the silencer 50 through the hydrogen vent valve 40. The conventional water trap device as described above has the following problems:
1) when the coolant left in the water trap is not removed due to a malfunction of the level sensor, it may deteriorate the performance of the fuel cell stack; and
2) since the hydrogen discharged through the anode outlet line has a pressure higher than the normal pressure, it requires the silencer for reducing discharge noise, the two level sensors, the moisture removal line connecting the anode outlet line to the water trap, thus increasing the manufacturing cost.
The information disclosed in this Background section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.